Context

We're seeing issues where discarding a prediction (e.g. editor::Cancel while a prediction is being shown) seems to just hide it temporarily. This is becoming a larger issue with #51842 as we now expect people to be dismissing predictions in order to insert literal tabs in certain contexts.
The logic changed in this PR is part of the problem, but the model generating the same prediction multiple times is also likely contributing. That will be solved as-needed later.

Self-Review Checklist

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Release Notes:

• Fixed an issue where dismissing an edit prediction would not fully discard it, causing it to re-appear